Coated fiber strands can be used in making a variety of products. For example, optical fibers typically comprise a fiber optic strand having one or more resin coating layers which protect the fiber from environmental conditions such as dust and moisture that can adversely effect its properties.
Examples of multiple coating layers for optical fibers are disclosed in U.S. Pat. Nos. 4,480,898; 4,474,830; 4,851,165; and 5,146,531 each of which are incorporated by reference in their entirety for all purposes.
These coating layers often include a first, or primary, coating layer directly applied to the glass fiber, which acts as a xe2x80x9cbufferxe2x80x9d to cushion and protect the fiber, and a secondary coating layer. The secondary coating layer typically functions as a protective outer layer preventing damage to the fiber during processing and use.
Because optical fiber coatings are typically clear, the resulting optical fiber is not colored. However, it is known to provide a colored coating and therefore a colored optical fiber. In this regard, a desired color is mixed into the prepolymer containing composition that forms the desired coating. This colored coating is then introduced as a substitute for the secondary coating or as an additional tertiary coating onto the fiber.
While this technique has allowed for the xe2x80x9ccoloringxe2x80x9d of fibers, it has introduced its own set of difficulties. For example, in processes which seek to cure both the primary and secondary coatings in a single curing step, the use of a colored secondary coating can adversely effect the cure of the inner or primary coatings and thus, lead to poor mechanical performance of the fiber.
Moreover, from a practical standpoint, insofar as a manufacturer must maintain a separate inventory for each of the colored coatings, inventory management is more complicated. For example, at least twelve different colors are employed in the field of telephony. Accordingly, to provide color fibers for use in such environments, manufacturers would be required to maintain a separate inventory for each of the desired colored secondary coatings.
The invention is based, at least in part, on the surprising discovery that one or more heterogeneous regions, e.g., coding stripes, can be introduced into or onto a coating layer on a fiber strand so as to provide for a desired functionality, e.g., coding of the fiber. Moreover, the region(s) can be introduced without adversely effecting subsequent processing steps used in making the fibers, e.g., curing of the coating layer(s).
One aspect of the present invention relates to a coated fiber which includes a fiber strand, at least one coating layer which is directly or indirectly on the strand, and at least one heterogeneous region present in or on one or more of the coating layer(s). A preferred embodiment of the invention involves the use of a primary coating layer and a secondary coating layer where the heterogeneous region(s) are in the secondary coating layer.
While the heterogeneous region(s) preferably comprise a colored material useful in color coding of the fiber, the region can be used to provide a number of desired functionalities to the resulting fiber.
Another aspect of the invention relates to a method for forming a coated fiber which includes introducing at least one coating layer onto a fiber strand such that the coating layer directly or indirectly covers at least a portion of the surface of the strand and introducing at least one heterogeneous region into or on one or more of the coating layer(s). The coated fiber can then be treated, e.g., cured so as to provide a desired product.
Once again, it is preferred that the method involves introducing a primary coating layer and a secondary coating layer onto a strand. The region(s) are preferably introduced simultaneously with or subsequent to the secondary coating layer prior to curing of the coating layer.